<script>
  const obj = {
    name: "djw",
  };
  if (obj.a == null) {
    console.log("obj.a=====", obj.a);
    console.log("null...");
  } else {
    console.log(obj.a);
  }
  const obj1 = {
    x: 100,
    y: 200,
  };
  const obj2 = obj1;
  let x1 = obj1.x;
  obj2.x = 101;
  x1 = 102;
  console.log(obj1);
</script>
